Employing the heating and cooling effect of a refrigerating cycle



United States Patent O 3,212,276 EMPLOYIN G THE HEATING AND COLlNG EFFECT F A REFRIGERATING CYCLE Aksel C. Eld, Mount Lebanon Township, Allegheny County, and William R. Lehrian, Penn Hills, Pa., as-

signors to Gulf Oil Corporation, Pittsburgh, Pa., a

corporation of Pennsylvania Filed Aug. 17, 1961, Ser. No. 132,216 Claims. (Cl. 62-21) This application is alcontinuation-in-part of our prior copending application, Serial No. 782,731, tiled December 24, 1958 and now abandoned.

This invention relates to an improved method and apparatusv for operating a refrigeration-heating system and more particularly to such a system employed in combination with a fractionation column for distillation of low boiling, narrow boiling range duid mixtures.

In separating low boiling, narrow boiling range fluid mixtures such as mixtures of normally gaseous hydrocarbons by fractional distillation it is necessary either to carry out the fractionation at very high pressure, employing ordinary cooling water to condense the overhead vapor, or to employ refrigeration for condensing the overhead vapor and carry out the fractionation at relatively low pressure. The lower pressure operation has advantages becausethe relative volatilities of liquids are usually much greater at low pressures than at high pressures so that a column with fewer plates and a lower reflux ratio can be used than could be used for the same degree of separation at higher pressure. Consequently, the use of refrigeration equipment for cooling the overhead vapor to a low temperature sullicient for condensation at the lower pressure has become well known. It is expensive to refrigerate the overhead condenser of a fractionating column and various proposals have been made for improving the economics of the refrigeration stage. For instance, it has been proposed to employ refrigeration-heating systems by means of which heat withdrawn from the overhead vapor in the refrigeration stage is used to reboil the column or, in other words, to supply heat to liquid in the bottom of the fractionating column. In this type of operation the overhead vapor is cooled and condensed by heat exchange with an evaporating refrigerant. The refrigerant vapor, containing heat absorbed from the column overhead vapor, is then compressed, its temperature thereby being raised above the temperature of the bottom of the fractionating column. The compression-heated vapor is then heat exchanged with liquid in the bottom of the fractionating column to reboil the column.

In commercial operation of fractionating columns the composition and the amount of the feed to the column may fluctuate considerably. Because of these iluctuations, the systems for expansion cooling and compression heating require additional means for adjusting to changes in the heating and cooling requirements of the column. However, all of the systems have certain disadvantages. In some systems the disadvantages reside in excessive evolution of heat` by compression and wasteful dissipation of heat during periods when the heating requirements of the column are reduced. Others have disadvantages of poor sensitivity of control in adjusting to meet the changing needs of the fractionation.

A refrigeration-heating system has now been developed employing expansion cooling and compression heating which is especially adapted for use in the fractional distillation of low boiling, narrow boiling range uid mixtures such as mixtures of hydrocarbons in the C1-C5 range when employing refrigeration for condensing the overhead vapor. The novel methods and apparatus of this invention have important advantages in the ease of adjustment to changing cooling requirements of the material to be 37,212,276 Patented Oct. 19, 196.5

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cooled and changing heating requirements of the material to be heated, and are adapted to provide efficient and sensitive automatic balance ofthe heating and cooling loads.

This invention relates to a method and apparatus for operating a refrigeration-heating system comprising at least one cooling and at least one heating zone. Inmaccordance with the invention liquid refrigerant is removed from a common accumulating vessel and is sent to the cooling zone where the liquid refrigerant is converted to a refrigerant vapor While being heat exchanged with material to be cooled. The refrigerant vapors are thereafter compressed and thus heated in a Vlow pressure compression zone. The compression heated refrigerant vapors are condensed by heat exchange with material to be heated in the heating zone. The condensed refrigerant vapors are thereafter sent to the common accumulating vessel and a constant liquid level is maintained the common accumulating vessel to insure suicient refrigerant for heating and cooling purposes. In one embodiment of this invention, wherein the liquid level in the common accumulating vessel tends to fall, a portion of the compressed refrigerant vapors from the low pressure compression zone are further compressed in a high pressure compression zone to a pressure suflicient to condense the further compressed refrigerant vapors at the temperature of a relatively high temperature coolant, and wherein said further compressed refrigerant vapors are condensed to the liquid phase by heat exchange with the relatively high temperature coolant. In yet another embodiment of this invention, wherein the.. liquid level in said common accumulating vessel tendsy to'rise, a portion of the liquid in said common accumulating vessel is vaporized and passed to said low pressure compression zone so as to maintain a constant liquid level in said common accumulating vessel. i

The apparatus for use in the refrigeration-heating system of this invention comprising in combination a low pressure refrigerant vapor compressor and a high pressure refrigerant vapor compressor, a line for deliveing a portion of the compressed refrigerant vapor from the low pressure compressor to the high pressure compressor for further compression thereby, means for delivering another portion of the compressed refrigerant vapor from the low pressure compressor to the hot side of a heat exchanger, a rst valve means for controlling the rate of ilow of cornpressed refrigerant vapor from the low pressure compressor to said heat exchanger in response to the heating needs of material on the cold side of said heat exchanger, a common accumulating Vessel for receiving condensed refrigerant from the hot side of said heat exchanger, a water cooled condenser, a line for delivering further compressed vapor from the high pressure compressor to said water cooled condenser, means for condensing said further compressed vapor by said water cooled condenser, a line for delivering condensed refrigerant liquid from said water cooled condenser to said common accumulating vessel, a vapor line for delivering vapor from said common accumulating vessel to said low pressure compressor, valve means in said vapor line for controlling the total pressure in said common accumulating vessel, a line for delivering iquid from said common accumulating vessel to the cold side of a heat exchanger, valve means in said line for controlling the rate of delivery of liquid to said latter heat exchanger in response to the cooling needs of material on the hot side of said exchanger, a liquid level controller associated with said common accumulating vessel, said controller being adapted to control the delivery of 10W pressure refrigerant vapors to said high pressure compressor and said controller being adapted to control the operation of said high pressure compressor in response to decreases in liquid level in said common accumulating vessel, and a liquid level controller associated with said common accumulating vessel, said controller being adapted to control the degree of opening of the valve means in the vapor line from said common accumulating vessel in response to increases in liquid level in said common accumulating vessel.

The invention will be described in more detail by reference to the gure which is a schematic diagram of one embodiment of the method and apparatus of the invention employed in combination with a fractionating column.

The figure shows a use for which the refrigerationheating system is particularly adapted, namely, for providing heating and cooling in the fractional distillation of a low boiling, narrow boiling range fluid mixture. Referring to FIGURE l, the liquid feed, such as an ethyleneethane mixture, is charged via line to the fractionating column 12. Liquid withdrawn from the bottom of the column via line 14 is passed via line 14 to the cold side (usually the shell side) of reboiling heat exchanger 16 where it is heated by indirect heat exchange with compression heated refrigerant which flows on the hot side (usually the tube side) of reboiler or heat exchanger 16. The bottoms liquid from line 14 is heated to a temperature above the bubble point of the ethylene-ethane charge mixture. That portion of the heated bottoms liquid which is heated is returned to the fractionating column by line 18 to reboil the column. Another portion of the bottoms liquid is withdrawn by line 14 through valve 20 as the ethane bottoms product. Overhead vapor is withdrawn from the column via line 22 and is passed to the hot side (usually the tube side) of condenser 24, where it is cooled by indirect heat exchange with an evaporating refrigerant on the cold side (usually the shell side) of the condenser. The condensed overhead vapor enriched in ethylene is collected in drum 26. A portion of the condensate from drum 26 is returned to the column as redux by line 28 and pump 29 and another portion is withdrawn by line 30 as the ethylene overhead product. The rate of withdrawal through line 30 is controlled by the valve 32 which is in turn controlled by liquid level controller 33 through air line 35 so as to maintain a constant liquid level in drum 26.

The rate of cooling in the overhead condenser 24 is controlled in response to the cooling needs of the fractionating columns 12. More particularly the cooling rate is controlled in response to measurement of a fractionation variable that is indicative of the composition of a fractionating column vapor or liquid stream. As will be explained subsequently, other variables can be chosen for this measurement, but temperature within the column is a convenient indicator of fractionating column stream composition. In the embodiment of the drawing, overhead cooling rate is controlled automatically in response to measurement of temperature within the column. The variable selected for measurement preferably is measured at a point in the column where the variable is changing most rapidly as an indication of overhead product composition. Temperature is preferably measured near the top of the column. In the embodiment of FIGURE 1, the temperature is measured near the top of column 12, employing a temperature controller 34 which operates valve 36 in line 38 which delivers refrigerant to the overhead condenser 24.

The control of valve 36 is accomplished by means of a temperature sensitive or detecting device positioned near the top of column 12 and associated with temperature controller 34. Temperature measuring and controlling devices of this kind are well known and include such instruments as industrial thermometers, bimetallic thermometers, thermocouples, and the like. The process and apparatus of this invention are not meant to be limited to the use of any particular type of device.

The temperature controller 34 is connected to valve 36 by pneumatic or capillary tubing or by electrical conductors, Whichever is appropriate for the particular device. The iiow control valve 36 is an automatically controllable valve such as a pneumatic diaphragm motor operated valve or an electric motor operated valve, or the like. Advantageously, as shown in the drawing, valve 36 is a diaphragm valve which is operated pngmatically by the temperature controller 34 through air line 40. l

Normally the refrigerent from lines 42 and 38 is introduced to the shell side of the condenser and the overhead vapor from line 22 flows through the tubes of the condenser. The pressure on the liquid refrigerant in lines 42 and 38 is reduced at valve 36 and the refrigerant evaporates at the lower pressure maintained in the shell of condenser 24. The remaining liquid refrigerent on the shell side of the condenser is cooled to a low temperature by the vaporization. The overhead vapor from line 22 which passes through the tubes of condenser 24 is colled and condensed by indirect heat exchange with the cold evaporating refrigerant liquid. Preferably, a high level of liquid is maintained on the shell side of the condenser so as to provide a large surface of heat exchange contact between the cold refrigerant liquid and the tubes.

Valve 36 is operated by temperature control-ler 34 in response to changes in the temperature near the top of column 12. The rate of flow of refrigerant through valve 36 is increased as the temperature near the top of the column tends to rise, and is decreased as the temperature near the top of the column tends to fall. In this way, the supply of refrigerant is automatically adjusted to the changing cooling requirements of the column.

The expanded refrigerant vapor, containing heat recovered from the overhead vapor from column 12,`

is withdrawn from condenser 24 by line 44 and is passed to drum 46. This drum separates any entrained liquid from the refrigerant vapor and is advantageously provided with a steam coil 48 for heating the refrigerant to aid in vaporizing entrained liquid. The refrigerant vapor then passes by line 50 to a low pressure compressor 52. This compressor is operated at a constant speed by a steam turbine 54. The refrigerant vapor from line 50 is compressed by compressor 52 to a pres sure sufficient to raise the temperature of the compressedl vapor above -the bubble point of the ethylene-ethane mixture charged to column 12. The compression heatedvapor is withdrawn by line 56 and a portion thereof is passed by lines 58 and 60 to the reboiling heat exchanger 16. Compression heated refrigerant vapor thus supplies reboiling heat to the bottoms liquid of column 12.

Another portion of the compression heated vapor from the low pressure compressor 52 is passed by line 62 through valve 63 to the high pressure compressor 64 and is further compressed to a higher pressure. Compressor 64 operates intermittently but at such a speed that a desired uniform outlet pressure is obtained. Compressor 64 is run by a steam turbine 66 which is operated only when valve 68 is opened which will be more fully described hereinafter. The further compressed refrigerant vapor is withdrawn from compressor 64 by line 70 and is at a pressure suiciently high to cause condensation of the refrigerant when heat exchanged with a relatively high temperature coolant such as ordinary cooling water. The further compressed vapor passes to condenser 72v which is cooled by cooling water introduced to the cold side of condenser 72 by line 74 at a temperature, for example, of F.

The condensed refrigerant is withdrawn from condenser 72 by line 76 and is collected in the drum or accumulating vessel 78.

Liquid is withdrawn from drum 78 by line 86 and. is passed to a common accumulating vessel 88. Drum- 78 is provided with a liquid level controller 90 of conventional design which operates the diaphragm valve 92 to release liquid through line 86 at such a rate as to maintain a constant liquid level in drum 78.

vessel 88.

As has been indicated, the compression-heated refrigerant vapor from the low pressure compressor 52 passes by lines 58 and 60 to the reboiling heat exchanger 16. The rate of heat exchange with the bottoms lliquid from column 12 in exchanger 16 is controlled in accordance with the heat requirements of the column as indicated by measurement of a selected condition within the column, for instance, by measurement of temperature at a point near the bottom of the column. In the embodiment of VFIGURE 1, column 12 is provided with a temperature controlling device 96 which `operates valve 98 in response to changes in temperature in the bottom of column 12. As the temperature in the bottom of column 12 tends to fall below a preset value, the temperature controller 96 automatically controls the diaphragm valve 98 by air line 100 to increase the rate of flow of reboiling refrigerant withdrawn from reboilin-g heat exchanger 16. This increases the flow of the compression-heated vapor to the reboiler 16 by way of line 60 and increases the heat content of the vaporized bottoms liquid returned to column 12 by line 18. Similarly, if the temperature near the bottom of the column 12 tends to rise, the

Yow of hot compressed refrigerant or reboiling medium is decreased by control of valve 98.

The hot compressed refrigerant vapor is cooled and condensed as a result of the heat exchange with bottoms liquid in reboiler 16. The condensate passes by line V102 to the common accumulating vessel 88.

The common accumulating vessel 88 is provided with a line 106 kby means of which refrigerant vapor is withdrawn and passed to the low pressure compressor 52. Valve 108 is placed in line 106 and controls the total pressure in the common accumulating vessel 88. Valve 108 is also an automatically controllable valve similar to valve 36.

The common accumulating vessel 88 is also provided with a liquid level controller 104, which controls the vopening of valves 63, 68 and 108. The control of valve 63 regulates the delivery -of Ilow pressure refrigerant vapors to the high pressure compressor 64. The control of lvalve 68 regulates the operation of compressor 64 via the operation lof the turbine 66. Control of both valves 63 and 68 ultimately regulates the amount of refrigerant liquid delivered to the common accumulating vessel 88-through line 86. The control of valve 108 controls the total pressure in the common accumulating vessel which in turn regulates the amount of vaporization of the refrigerant liquid in the common accumulating In the embodiment shown in FIGURE l, valve 108 is a diaphragm valve which is operated pneumatically through air line 110 in respon-se to level controller 104. The vapor in line 106 passes by way of liquid disengaging drum 114 which is provided with a steam coil 116 to aid in vaporization of entrained liquid before return of the vapor by line 118 to compressor 52. This liquid disengagaing drum 114 and the drum f other vnon-refrigerant liquids that might be present in the system.

The operation of the refrigeration-heating system was generally described above. The system is designed to meet the cha-nging'heating and cooling requirements of the fractionating column, for example, to which it is attached.

The liquid level controller 104 can be set to control the lliquid level in the common accumulating vessel 88 at any desired point.

The liquid level in the common accumulating vessel 88 will tend to fall below the set point either because of increased cooling requirements of the cooling zone, wherein more refrigerant liquid will be removed from the common accumulating vessel 88 and delivered to the cooling zone through line 42, or decreased heating requirements of the heating zone, wherein less liquid is added to the common accumulating vessel 88 through line 102. As the liquid level in 88 begins to fall below the set point, level controller 104 will close valve 108 (if it were open) and open valve 63 and steam valve 68 to operate the compressor 64 and allow a port-ion of the low pressure refrigerant vapors to enter the compressor 64 via line 62. The outlet pressure of the high pressure compressor 64 isl sufficiently high to cause condensation of the further compressed refrigerant vapors in heat exchanger 72. The condensed liquid from the heat eX- changer 72 flows through line 76 to drum 78 which causes the liquid level in drum 78 to begin to increase. Level controller will operate valve 92 to increase the rate of withdrawal of liquid from drum 78 through line 86. The increased flow of refrigerant liquid through line 86 is delivered to the commonaccumulating vessel 88 and thus the fall of liquid level in 88 is checked.

On the other hand, the liquid level in the common accumulating vessel 88 may tend to rise above the set point of the liquid level controller 104 either because of--decreased cooling requirements of the cooling zone, Wherein less refrigerant liquid will be removed from the common accumulating vessel 88 and delivered to the cooling zone through line 42, or increased heating requirements of the heating zone, wherein more liquid is added to the common accumulating vessel 88 through line 102. As the liquid level in 88 begins to rise, level controller 104 operates to close valves 63 and 68 (if they were open) and open valve 108. By closing valves 63 and 68 (if they are open) the ow :of condensed liquid refrigerant from the heat 4exchanger 72 through line 76 to drum 78 is shut olf. As a consequence, the liquid level in drum 78 will begin to decrease. As the liquid level in drum 78 decreases, level controller 90 operates to close valve 92 to decrease the rate of withdrawal of refrigerant liquid from drum 78 through line 86.

At the same time, valve 108 has been opened. to reduce the total pressure in the commonaccumulating vessel 88 and thus vaporize a portion of the refrigerant liquid in vessel 88. The vapors from vessel 88 pass through line 106, drum 114, and line 118 to the low pressure compressor 52.

If the rate of withdrawal of refrigerant liquid from the common accumulating vessel 88 to `the cooling zone through line 42, and the rate of addition of refrigerant liquid from the heating zone to the common accumulating vessel 88 through line 102 are such as to maintain the liquid level in 88 at the desired set point on level controller 104, then valves 63, 68 Iand'108 will all remain closed.

The embodiment of the method of this invention shown r1n FIGURE l has the important advantage of economy of `operation of the high pressure compressor. Instead 'of operating continuously, the high pressure compressor 64 operates only intermittently to adjust lfor affalling liquid level in the common accumulating vessel 88. A considerable savings in power can thus lbe realized. 'In addition to this unique advantage, the embodiment of FIGURE l also 'has another advantage. Thus, the heating of a fractionating column is accomplished with the system of this invention 'by compressing the expanded refrigerant to only a rather low'pressure and thereafter condensing the required amount of compressed refrigerant in the heating zone. Additional condensation of the compressed refrigerant if required is accomplished Aby cooling with cheap cooling water instead of with -a low temperature refrigerant. This is made possible by compressing the required amount of the expanded refrige ant vapor to -a sufficiently high pressure to achieve condensation at the relatively high temperature of ordinary cooling water. Control `of the amount of further compression is accomplished through the use of a liquid level controller, the latter having important advantages of sensitivity of control and simplicity of operation.

The refrigeration-heating system of the invention can be used for a number of refrigeration land heating purposes in addition to supplying the heating land cooling needs of a fractionating column. Furthermore, the method and apparatus of the invention can be used for fractional distillation of a considerable number of low boiling point, narrow boil-ing range fluid mixtures. However, further understanding of the method and apparatus of the invention can be gained from consideration of possible conditions and results in the fractionation of an ethylene-ethane mixture which will be described as an illustration of a specific use of the process. The table below gives, as an illustration, the charge and product rates for the frationation of a typical ethylene-ethane mixture in accordance with the invention.

The ethylene-ethane charge at the rates indicated in the table is introduced at a temperature of F. to column 12, the temperature at the top of the column being 11 F. and the pressure 325 pounds per square inch absolute (abbreviated hereinafter as p.s.i.a.) and the temperature at the bottom of the column being 9 F. and the pressure 335 p.s.i.a. The refrigerant is a mixture composed of 10 mole percent ethane, 50 mole percent propane and 40 mole percent n-butane. The expanded refrigerant vapor from condenser 24 enters the compressor 52 by line 50 at a temperature of 35 F. and a pressure of 20 p.s.i.a. Vapors from the common accumulating vessel 88 via the disengaging drum 114 enter the compressor 52 at a higher stage than line 50 by line 118 at a temperature of 50 F. and a pressure of about 90 p.s.i.a. The vapor is compressed in compressor 52 and is discharged by line 56 at a temperature of 100 F. and a pressure of 100 p.s.i.a. The low pressure vapors are then passed to reboiling heat exchanger 16 via lines 58 and 60. When required, another portion of the low pressure vapors is passed to the high pressure compressor 64. In FIGURE l, compressor 64, which compresses the vapor from line 62, operates at a constant speed and in the specific operation under consideration the outlet pressure of the vapor in line 70 will be about 300 p.s.i.a. Cooling water is introduced to condenser 72 at 95 F. and the cooled condensed refrigerant is withdrawn from condenser 72 by line 76 at a temperature of about 110 F.

In the example above, a Cz-C.,A hydrocarbon mixture was used as the mixed refrigerant. A number of other refrigerant mixtures can also be used, such as C3-C5, and C1-C5 hydrocarbon mixtures. Propane is an example of a suitable pure compound refrigerant. Other pure compound refrigerants include ammonia and freon, in addition to other pure hydrocarbons, such as ethane, ethylene and butane.

The novel methods and apparatus of the invention have the important advantage of adaptability to the use of automatic controls for indicating changes in the heating and cooling loads to which the system must adjust, but it should be understood that the invention is not meant to be limited to the use of automatic controllers. For any use of the refrigeration-heating system of this invention,

, changes in the heating and cooling needs can be indicated temperature near the top and near the bottom of column 12 can be operated manually or by automatic devices other than temperature controllers.

The measurement of temperature near the top and near the bottom of the fractionating column 12 has specifically been disclosed for controlling the cooling and heating loads of the refrigeration-heating system. As has been indicated, any variable that is indicative of stream composition within the column can be measured for the purpose of control of a fractionating column in accordance with the invention either automatically or manually. For instance, measurements of differential vapor pressure of streams Within the column and direct measurement of stream composition, for example, by means of an infrared analyzing controller, can be used in accordance with the invention for indicating the heating or cooling needs of the column.

In the foregoing description of the method and apparatus of the invention the use of two compressors in series was described. Instead of employing two compressors, a single compressor can be employed having a series of compression stages at successively higher pressures. Therefore, when reference is made to further compression of a portion of the compressed refrigerant vapor or to a low pressure and a high pressure compressor, such reference is meant to include the use either of a plurality of compressors or a single compressor having a plurality of compression stages.

In addition, the embodiment of the invention shown in FIGURE l shows the use of one liquid level controller 104 on the common accumulating vessel 88 which serves the dual function of opening valve 108 when the liquid level in 88 rises above a desired set point and opening valves 63 and 68 when the liquid level in 88 falls below a desired set point. If desired, separate liquid level controllers can be employed to open and close the various valves.

Still another possible modification of the method and apparatus illustrated in the drawing is the elimination of accumulating vessel 78. The function of this vessel is to control the ow of condensate to the accumulating vessel 88. However, means other than a vessel, such as drum 78, can be used for this purpose. For instance, the condensate can be passed directly from the shell side of condenser 72 to the common accumulating vessel 88, the shell side of the condenser being provided with a level controller such as shown for drum 78 in FIGURE 1.

Still a further modification of the method and apparatus illustrated in the drawing is the elimination of valve 63 in line 62. The function of valve 63 is to control the flow of vapors from the low pressure compressor 52 to the high pressure compressor 64 in response to decreases in the liquid level in vessel 88. Compressor 64 only operates when steam valve 68 is opened. Steam valve 68 only opens in conjunction with valve 63 in response to decreases in liquid level in vessel 88. Valve 63 is therefore a protective valve for compressor 64 so that when the compressor 64 is not operating, there will be no pressure in line 62 continuously pressing on the inlet of compressor 64. In a similar manner, a protective valve (not shown in FIGURE l) could be placed in line 70 or 76 to protect the outlet of compressor 64. This valve would operate in a manner similar to the operation of valves 63 and 68.

It should be noted also that the refrigeration-heating system can service a plurality of heating and cooling loads. Thus, as shown in FIGURE 1, liquid refrigerant can be passed by line through valve 132 to an additional cooling load, the expanded vapor being returned by line 134 and the compression-heated vapor can be passed to another heating load by line 136 through valve 138, the condensate being returned by line 140.

Resort may be had to such variations and modifications as fall wit-hin the spirit of the invention and the scope of the appended claims.

We claim:

1. A method of operating a refrigeration-heating plant which comprises at least one cooling and at least one heating zone comprising removing liquid refrigerant from a common accumulating vessel in response to the cooling requirements of the cooling zone, converting said` liquid refrigerant to a refrigerant vapor in said cooling zone, thereafter compressing and thus heating said refrigerant vapor in a compression zone, passing said compression heated refrigerant vapor to the heating zone, condensing the compression heated refrigerant vapors in said heating zone, passing the condensed refrigerant vapors from said heating zone to the common accumulating Vessel, further compressing a portion of thecompressed refrigerant vapors in response to decreases in liquid. level-in said common accumulating vessel, said further compression being at a pressure suicient toY condense the further` compressed refrigerant vapors at the temperature of a relatively high temperature coolant, condensing said'further compressed refrigerant vapor to the liquid phase by heat exchange with said relatively high temperature lcoolant and passing said condensed further compressed refrigerantvapors Yto said common accumulating vessel so as to maintain a constant liquid level in said commonr accumulating vessel.

2. A method of operating a refrigeration-heating plant which comprises at least one coolingand at least one heating zone comprising removing liquid .refrigerant from a common accumulating vessel in response to the cooling requirements of the cooling zone, converting said liquid refrigerant to a refrigerant vapor in said cooling zone, thereafter compressing and thus heating said refrigerant vapor in a compression zone, passing said compression heated refrigerant Vapor to the heating zone in response to the heating requirements of said heating zone, condensing the compression heated refrigerant vapors in said heating zone, passing the condensed refrigerant vapors from said heating zone to the common accumulating vessel, vaporizing a portion of the liquid in said common accumulating vessel in response to increases in liquid level in said common accumulating vessel so as to maintain a constant liquid level in said common accumulating vessel and passing the vapors from said common accumulating vessel to said compression zone.

3. The improvement according to claim 2 in which the refrigerant is a mixture of hydrocarbons having between l and 5 carbon atoms per molecule and in which the degree of vaporization of the refrigerant liquid in the common accumulating vessel is controlled by varying the total pressure in the common accumulating vessel.

4. The fractionation process which comprises fractionally distilling an ethylene-ethane mixture in a fractionating column, recovering an ethylene-rich overhead vapor stream and an ethane-rich bottoms liquid, condensing the overhead vapor stream by heat exchange in an overhead vapor condensing zone With an evaporating refrigerant, in a low pressure compression stage compressing refrigerant vapor Withdrawn from heat exchange with the overhead vapor to a pressure sufficient to raise the temperature of said refrigerant vapor above the bubble point of the et-hylene-ethane mixture, delivering at least a portion of the compression heated vapor from the low pressure compression stage to a reboiling zone Afor heat exchange with bottoms liquid of the fractionating column at a rate controlled in response to the heating needs of the column and thereby cooling and condensing the compressed refrigerant vapor, delivering the condensed-compressed refrigerant vapor from said reboiling zone to a common accumulating vessel, delivering refrigerant liquid from said common accumulating vessel to said overhead vapor condensing zone at a rate controlled in response to the cooling needs of the fractionating column, and maintaining a constant liquid level in said common accumulating vessel.

5f The process according to claim 4 wherein the liquid level in said common accumulating vessel tends to fall below a desired level and wherein a portion of the compression heated vapor from the low pressure compression stage is further compressed in a high pressure compression stage to a pressure suiciently high to condense said further compressed vapor at the temperature of ordinary cooling water, cooling said further compressed refrigerant vapor by heat exchange with vcooling Water to condense said vapor,collecting condensate from the cooling of the further compressed vapor in an accumulating vessel, delivering liquid from said accumulating Vessel to said common accumulating vessel -at arate controlled to maintain a constant liquid level in said accumulating vessel and controlling the operation of the high pressure compressor in response to decreases in liquidlevel in said common accumulating vessel.

6. The process according to claim 5 wherein the rate of delivery of compression heated vapor to the reboiling zone is controlled in response to measurement of temperature near the bottom ofthe fractionating column, said rate being increased vassaid temperature tends to fall and decreased as said temperature tends to rise, and

'wherein the rate of'` delivery of refrigerant'to the overhead .condensing zone is controlled` in response to measurement of temperature near the top of the fractionating fall.

7. In a refrigeration-heating apparatus the combination comprising a loW pressure refrigerant vapor compressor and a high pressure refrigerant` vapor cornpressor, means vfor delivering a portion of the compressed refrigerant vapor from the 10W pressure compressor to the high pressure compressor for further compression thereby, means for delivering another portion of the compressed refrigerant vapor from the low pressure compressor to the hot side of a heat exchanger, a rst valve means for controlling the rate -of flow of compressed refrigerant vapor from the low pressure compressor to said heat exchanger in response to the heating needs of material on the cold side of said heat exchanger, a common accumulating vessel for receiving condensed refrigerant from the hot side of said heat exchanger, a water cooled condenser, a line for deliver-ing further compressed vapor from the high pressure compressor to said water cooled condenser, means for condensing said further compressed vapor by said Water cooled condenser, a line for delivering condensed refrigerant liquid from said water cooled condenser to said common accumulating vessel, a vapor line for delivering vapor from said common accumulating vessel to said low pressure compressor, valve means in said vapor line for controlling the total pressure in said common accumulating vessel, a line for delivering liquid from said common accumulating vessel to the cold side of a heat exchanger, valve means in said line for controlling the rate of delivery of liquid to said latter heat exchanger in response to the cooling needs of material on the hot side of said exchanger, and a liquid level controller associated with said common accumulating vessel, said controller being adapted to control the operation of the high pressure compressor in response to decreases in liquid level in said common accumulating vessel, and said controller being adapted to control the degree of opening of the valve means in the vapor line from said common accumulating vessel in response to increases in the liquid level in said common accumulating vessel.

8. Apparatus according to claim 7 in which said liquid level controller of said common accumulating vessel is operatively connected with means for controlling the speed of said high pressure compressor.

9. Apparatus according to claim 7 in which the means for delivering a portion of the compressed vapor from the low pressure compressor to the high pressure compressor for further compression thereby, comprises a line with a valve means therein, said liquid level controller associated with said common accumulating vessel being adapted to control the opening of said valve means in response to decreases in liquid level in said common accumulating vessel. i

10. In a refrigeration-heating apparatus the combination comprising a low pressure refrigerant vapor compressor and a high pressure refrigerant vapor compressor, means for delivering a portion of the compressed refrigerant vapor from the low pressure compressor to the high pressure compressor for further compression thereby, means for delivering another portion of the compressed refrigerant vapor from the low pressure compressor to the hot side of a heat exchanger, a rst valve means for controlling the rate of flow of compressed refrigerant vapor from the low pressure compressor to said heat exchanger in response to the heating needs of material on the cold side of said heat exchanger, a common accumulating vessel for receiving condensed refrigerant from the hot side of said heat exchanger, a water cooled condenser, a line for delivering further compressed vapor from the high pressure compressor to said water cooled condenser, means for condensing said further compressed vapor by said water cooled condenser, a line for delivering condensed refrigerant liquid from said water cooled condenser to said common accumulating vessel, a vapor line for delivering vapor from said common accumulating vessel to said low pressure compressor, valve means in said vapor line for controlling the total pressure in said common accumulating vessel, a line for delivering liquid from said common accumulating vessel to the cold side of a heat exchanger, valve means in said line for controlling the rate of delivery of liquid to said latter heat exchanger in response to the cooling needs of material on the hot side of said exchanger, and a rst liquid level controller associated with said common accumulating vessel, said first liquid level controller being adapted to control the operation of the high pressure compressor in response to decreases in liquid level in said common accumulating vessel, and a second liquid level controller associated with said common accumulating vessel, said second liquid level controller being adapted to control the degree of opening of the valve means in the vapor line from said common accumulating vessel in response to increases in the liquid level in said common accumulating vessel.

References Cited by the Examiner UNITED STATES PATENTS 2,133,962 10/38 Shoemaker 62-199 2,453,033 11/48 Patterson 62-510 X 2,534,274 12/50 Kniel 62-40 X 2,619,814 12/52 Kniel 62-31 X 2,645,104 7/53 Kniel 62-31 X 2,916,888 12/59 Cobb 62-34 X 2,933,901 4/60 Davison 62-37 2,984,988 5/61 Berger 62-37 X 3,018,640 1/62 Heller 62--510 X FOREIGN PATENTS 656,641 1/29 France. 338,283 6/21 Germany.

NORMAN YUDKOFF, Primary Examiner.

ROBERT A. OLEARY, Examiner.

UNITED STATES l,PATENT OFFICE ma CERTIFICATE OF CORRECTION Patent No 3 212 276 October 19, 1965 Aksel C. Eld et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 40, for "deliveng" read delivering column 3, line 18, for "14", second occurrence, read 15 line 44, for "columns" read column column 4, line 6, for "refrigerent" read refrigerant line 16, for "colled" read Cooled column 5, line 56, for "disengagaing" read dsengaging Signed and sealed this 27th day of September 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A METHOD OF OPERATING A REFRIGERATION-HEATING PLANT WHICH COMPRISES AT LEAST ONE COOLING AND A LEAST ONE HEATING ZONE COMPRISING REMOVING LIQUID REFRIGERANT FROM A COMMON ACCUMULATING VESSEL IN RESPONSE TO THE COOLING REQUIREMENTS OF THE COOLING ZONE, CONVERTING SAID LIQUID REFRIGERANT TO A REFRIGERANT VAPOR IN SAID COOLING ZONE, THERAFTER COMPRESSING AND THUS HEATING SAID REFRIGERANT VAPOR IN A COMPRESSION ZONE, PASSING SAID COMPRESSION HEATED REFRIGERANT VAPOR TO THE HEATING ZONE, CONDENSING THE COMPRESSION HEATED REFRIGERANT VAPORS IN SAID HEATING ZONE, PASSING CONDENSED REFRIGERANT VAPORS FROM SAID HEATING ZONE TO THE COMMON ACCUMULATING VESSEL, FURTHER COMPRESSING A PORTION OF THE COMPRESSED REFRIGERANT VAPORS IN RESPONSE TO DECREASES IN LIQUID LEVEL IN SAID COMMON ACCUMULATING VESSEL, SAID FURTHER COMPRESSION BEING AT A PRESSURE SUFFICIENT TO CONDENSE THE FURTHER COMPRESSED REFRIGERANT VAPORS AT THE TEMPERATURE OF A RELATIVELY HIGH TEMPERATURE COOLANT, CONDENSING SAID FURTHER COMPRESSED REFRIGERANT VAPOR TO THE LIQUID PHASE BY HEAT EXCHANGE WITH SAID RELATIVELY HIGH TEMPERATURE COOLANT AND PASSING SAID CONDENSED FURTHER COMPRESSED REFRIGERANT VAPORS TO SAID COMMON ACCUMULATING VESSEL SO AS TO MAINTAIN A CONSTANT LIQUID LEVEL IN SAID COMMON ACCUMULATING VASSEL. 